Video Synthesizer - Evolution Into Frame Buffers

Evolution Into Frame Buffers

Video synthesizers moved from analog to the precision control of digital. The first digital effects as exemplified by Stephen Beck's Video Weavings used digital oscillators optionally linked to horizontal, vertical, or frame resets to generate timing ramps. These ramps could be gated to create the video image itself and were responsible for its underlying geometric texture. Schier and Vasulka advanced the state of the art from address counters to programmable (microcodable) AMD Am2901 bit slice based address generators. On the data path, they used 74S181 arithmetic and logic units, previously thought of as a component for doing arithmetic instructions in minicomputers, to process real time video signals, creating new signals representing the sum, difference, AND, XOR, and so on, of two input signals. These two elements, the address generator, and the video data pipeline, recur as core features of digital video architecture.

The address generator supplied read and write addresses to a real time video memory, which can be thought of as evolution into the most flexible form of gating the address bits together to produce the video. While the video frame buffer is now present in every computer's graphics card, it has not carried forward a number of features of the early video synths. The address generator counts in a fixed rectangular pattern from the upper left hand corner of the screen, across each line, to the bottom. This discarded a whole technology of modifying the image by variations in the read and write addressing sequence provided by the hardware address generators as the image passed through the memory. Today, address based distortions are more often accomplished by blitter operations moving data in the memory, rather than changes in video hardware addressing patterns.